Lighting for planting outdoors

By
Ed Rosenthal
on June 10, 2003

I am germinating seeds in soil under two 40-watt fluorescent tubes. I have my timer set to 16 hours on and eight hours off. I’m planning on putting them outside as soon as weather permits. Should I change my lighting or leave it like it is?
Meucci,
Internet

The seedlings should receive more intense light so that they will be somewhat acclimated to sunlight. Rather than fluorescent lighting you could use a small high intensity lamp such as a 250-watt high pressure sodium (HPS) lamp. The problem with both high energy lamps and fluorescents is that they don’t contain much ultraviolet light. This is the spectrum most likely to burn plants not acclimated to sunlight.

Placing the plants outdoors in filtered sunlight for a few days will help them adapt to the high energy spectrum. A partly shady space or a shade cloth gives the plants time to adjust to their new conditions.

The 18-6 flowering schedule is suitable for plants which are to be grown outdoors. That way they won’t be shocked into flowering when they are placed outdoors. Plants that are grown under continuous light will sometimes flower when they are placed outdoors because moving from continuous light to only 14-18 hours of light (depending on latitude) at the height of summer sometimes forces plants to flower prematurely. Plants grown under 17-18 hours of light adjust better to the outdoors and don’t flower until they are supposed to, in the fall.

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